1. Field of the Invention
This invention relates to focusing electrode structures for cathode ray tubes, and more particularly to focusing means in a multibeam in-line CRT electron gun assembly wherein efficient overlapping lenses are provided.
2. Prior Art
Advancements in cathode ray tube technology have fostered a trend toward miniaturization and compaction of electron gun structures, such structures in turn being encompassed within envelope neck portions of increasingly smaller diameters and shorter lengths. Consequently, the structural dimensions of the electrode elements of the gun assembly have been adapted to achieve the desired compaction. Such is especially evidenced in conventional in-line gun assemblies, wherein three separate electron beams emanate in a substantially common plane. This is conventionally accomplished by employing unit-type construction, wherein several functionally similar electrodes, ahead of individual cathodes, are combined as unitized structures to favor compaction.
In effecting miniaturization of in-line gun assemblies, factors influencing the quality of focusing of the individual electron beams become more critical as the diameters of the main focusing lenses, being positioned in-line in the horizontal plane of the assembly, are necessarily reduced to meet dimensional requirements. Consequently, the reduced in-line dimensioning tends to foster increased spherical aberration in the main focusing lenses. Thus, with such compaction of gun structures, it becomes much more difficult to consistently achieve the quality of efficient beam focusing needed to produce the desired small and round spot size beam impingement on the display screen.
Accordingly, objectives of the present invention include the provision of modified focusing electrode means for expeditiously effecting improved quality of beam focusing by reducing spherical aberration in the lenses or smaller types of in-line electron gun assemblies, such being accomplished while still achieving the desired in-line structural compaction. The improvement is realized in the unitized main focusing electrode structure which is discretely modified to beneficially accomodate lenses of larger diameters than commonly employed in a similar size structure.